A vacuum is space devoid of matter. The word is derived from the Latin adjective vacuus meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.

निर्वात स्थिती म्हणजे, ती जागा, ज्यात (हवेसकट) कोणताच पदार्थ नसणे. अशा स्थितीत जी पोकळी निर्माण होते त्यात वायूचा दाब वातावरणिय दाबापेक्षा बऱ्याच प्रमाणात कमी असतो. १००% निर्वात स्थिती ही जवळजवळ अशक्य असते. एखादी जागा अथवा पोकळी, फक्त काही प्रमाणातच निर्वात करता येऊ शकते.